Compressor And
       Pressure Issues

This page on compressor and pressure issues is one of a series that include questions and comments from site visitors, and the various responses provided to help them with their air compressor issues.

This is where you can post question of your own, or offer advice or a comment to an existing post.

Craftsman compressor Reed Valve Problem
Replacement-the next step?

By: Rob, from Alabama

Thanks for your great website. I have really been scratching my head about my compressor. A few minutes at the site has been a great help in narrowing down the problem.

compressor valve plate

I have a small Craftsman 921.153101--3 gal. 1.5hp unit. It will build pressure. I can hear it leaking--only when it is running. Your reed valve article sent me to check the intake filter assembly. When it is running, I can feel a steady stream of air pouring OUT of the intake.

I tore down the cylinder assembly and the reed valves are not damaged. Is there any easy to to assure that they're seated properly? Do I need to replace the assembly? Just the reeds and the valve plates? I've looked at the parts and (as you once again so wonderfully pointed out) it is not cost effective to send this out to the Sears repair service. The P&L would be as much or more than the unit. Thanks again for all you're doing. Keep up the great work!

My response: Great picture Rob, and thanks for the kind words. I expect that the reed valves are not working. Nope, I don't know the check for proper valve seating? Anyone else have any thoughts?

Comments: Check valve - by: Anthony

Had the same issue with my 5 hp belair. Turns out the check valve at the tank had failed and pressure pushing back into the compressor motor.

Comments: Craftsman 15310 - by: Kenney Yale. Rob I have the exact same compressor and am having issues with it building pressure. The gaskets look ok and are sealed tight, to my knowledge. There is oil. The only air I feel seems to be coming from the generator. I don't know even what the reed set up is supposed to be. Is it one reed per slot??? I have 2 reeds and 2 slots. It looks like they both fit in one slot. What did yours look like?

New Question about Emglo compressor does not build full pressure? By: al, US

My Emglo k15a-8p turns on but does not seem like it is running full speed. it builds pressure slowly and only up to around 80psi. I think it is setup as constant run as when it is full of air, it still runs, but something happens and it runs much quieter. Now the compressor runs in this "quiet" state all the time. any ideas?

My response about Emglo compressor Constant run compressors have valves that control the intake. When the pressure in the tank reaches cut-out pressure, then that valve opens, unloads the compressor, and the electric motor can run with almost no load, saving wear, tear and energy cost. If your compressor only runs "unloaded", then likely you've got a problem with the unloader circuit.

Can you refer to your manual, or contact the manufacturer? If not, it's off to your local Repair shop. See the Repairs page to see if a local repair shop has contact info for you.

New Question about Craftsman compressor won't build pressure? By: kenny Maldonado, colorado springs

I have a A craftsman 5 gallon 1 horse direct drive oil lubricated cast cylinder air compressor. I tried using two coil roofing nail guns on this compressor and now the thing doesn't even build any pressure, I've checked the release valve it's closed, exhaust seems to work right. what are your thoughts?

My Response: Why would you use two coil roofing nail guns on your poor compressor? What did it ever do to you? :-)

Am I to understand that you have connected two air guns from the compressor discharge coupling, and neither will run?

There are many reasons why a compressor will run yet not build pressure in the tank. And if there's no pressure in the tank, then the nail guns can't run. When the compressor shuts off (assuming it does) does air bleed out from the unloader valve constantly? That being the case, see the page On the other hand, if your compressor is running continuously and not gathering any pressure in the tank, then it won't ever reach cut out, and your unloader valve won't ever open, so you have a different problem. See the page, and see the link to pages about why an air compressor will not build air pressure.

Comments about Craftsman compressor won't build pressure?

Apr 17, 2011 - Check your gaskets - by: Anonymous

If your air compressor builds pressure to a point, and then won't go any higher, check your gaskets. If you take the compressor apart, be prepared to replace the gaskets as they are brittle after use and most likely will tear.

Check the gasket that divides the chambers by the air intake. Make sure that there is no part of the divider gasket missing. Even a small gap can cause pressure to cease building. You can buy replacement gaskets for most brands, or you can buy a sheet of gasket material at an auto parts store for under $10 and cut your own. Try to keep the old gaskets in tact as much as possible to use them as a template.

New Question about Hitachi air tank won't fill, compressor motor runs great?? By: Joseph Schneider, Duluth,Mn.USA

I have a Hitachi 2 HP 4 Gallon Oil-Lubricated Air Compressor Model # EC12.

hitachi air compressor

The motor sounds strong, but I'm getting hardly any air in my tanks. I check the oil and and looked at the gasket and it seems to look ok. Air is coming out of the top of motor. Don't know if that is normal.

My Response about Hitachi air tank won't fill Hello Joseph. No, air isn't supposed to come out of the top of the motor. This symptom makes me think that you have a valve failure, and what may be happening (since air follows the path of least resistance) is that the air that's being ingested by the compressor piston is being blown right back out the same inlet port since it's easier for the air to flow that way, than down past a check valve into the tank.

Why won't your compressor build air pressure? There are a list of reasons found at, though I suspect it's the reed valve that is causing your compressor problems.

Comments about Hitachi air tank won't fill Nov 18, 2009 - Hi bill - by: Joseph

Is the reed valve the cylinder shape by the gages that you can pull to release the air?

My Response No, that's the PRV, Joseph. The reed valves are located inside the intake hole (usually there is an intake filter screwed into the intake port) and they control the air in, and stop the air out, so that the air can be forced into the tank.